Append code to the end of an existing function

Question

I need to trigger function bar() whenever function foo() fires. I have no control over function foo or whether it will change in the future. I have this situation regularly (and

Answer 1

You can just override foo with a custom function that calls the original.

E.g.

var old_foo = foo;
foo = function() {
  old_foo();
  bar();
}

You should also pass any arguments foo takes into it via your replacement function.